In the manufacture of paper-pulp-insulated conductors, a plurality of conductors are moved into engagement with a rotatable drum for a portion of its rotation, while a pulpous mixture is deposited from a pulpous mixture distributor onto the drum and transferred to the conductors in the form of ribbons. A stationary vacuum box, located interiorly of the drum, causes the pulpous mixture from the distributor, which is referred to as a headbox, to be formed into ribbons on the drum and removes a large portion of their moisture content. See, for example, U.S. Pat. No. 1,765,533, issued to H. W. Jespersen on June 24, 1930. In another process, a pulpous mixture is transferred from a drum, which is mounted rotatably and submerged partially in a vat of the pulpous material, to conductors which are moved into tangential engagement with the drum. In either process, the pulp ribbons and conductors are then moved into engagement with an endless felt web which is passed between rolls to cause moisture to be removed from the pulp. Then the pulp ribbons and conductors are disengaged from the felt web and the pulp is subsequently formed into circular layers of insulation about the conductors.
The pulp ribbons produced by these prior art processes are not uniform in weight among all of the conductors, which results in changes in electrical properties of the conductors such as, for example, mutual capacitance when they are twisted together in pairs. Also, processes for pulp-insulating conductors have not been entirely successful in matching the velocity of the pulpous mixture with that of the cylinder at their confluence, notwithstanding the relatively low line speeds, e.g. 46 to 61 meters per minute (mpm), at which these processes are run. This affects elongation and tensile properties of the pulp insulation that are important because of the way in which the insulated conductors or cables are handled. If the velocity of the pulpous mixture leads that of the cylinder, a stagnation zone is established which results in fibers of the mixture having a random or so-called "cross-machine" orientation with decreased tensile strength; if it lags, the pulp fibers are oriented longitudinally, parallel to one another and have increased tensile strength but reduced elongation properties. Weight control of the pulpous mixture on the conductors is desirably accompanied by a suitable matching of the pulpous mixture and cylinder velocities to achieve an optimum combination of tensile and elongation properties.
The problem of non-uniform pulp weight has been overcome in the paper-making industry by the use of a blade valve which is capable of being moved closer to or farther from a bed and is adjustable along a continuous profile. The paper-making industry has also been successful in matching velocities of pulpous mixtures and cylinders by the use of the above-described blade valve, and in controlling the formation of relatively thick sheets by using a laminating procedure or a succession of headboxes.
However, nowhere has the prior art focused its attention on methods or apparatus which may be used to control the coating of strand materials with a pulpous mixture to achieve uniformly weighted pulp insulation having required elongation and tensile properties.